1. Field of the Invention.
The present invention relates to numerical control systems for driving motors in general and to a system for interfacing a resolver to such a control system in particular.
2. Description of the Prior Art.
Numerical control systems for controlling machine tools can be operated in either open-loop or closed-loop configurations. In the open-loop configuration, control signals are generated to drive means for moving the machine tool to a selected position. However, no check is made by the system to determine if the machine tool has actually reached the selected position. In the closed-loop system, a feedback signal representing the actual position of the machine tool is compared with a control signal representing the selected position to generate an error signal which is utilized to move the machine tool to the selected position.
A pair of synchros is among the most widely used error sensing devices in feedback control systems. One of the synchros has its rotor positioned so as to represent the selected position for the machine tool. An a.c. voltage is applied to the stator windings of this first or reference synchro which are connected to the stator windings of the second or control synchro. If the rotor of the control synchro is not rotationally aligned with the rotor of the reference synchro, an error voltage is generated. If the control synchro rotor position represents the actual position of the machine tool, the error signal can be utilized to position the machine tool.